Transcriptome analysis reveals the involvement of nitrate transporters in regulating strawberry fruit development

Abstract

Adequate nitrate availability throughout the strawberry life cycle improves fruit quality and productivity. However, the gene expression and metabolism patterns during nitrate-triggered developmental processes in fruits remain unknown. This transcriptome study reports the involvement of nitrate transporters and their correlated transcription factors (TFs) in the coordinate regulation of strawberry fruit development after nitrate treatment. Nitrate supply promoted plant growth and slightly delayed fruit ripening compared with the control. Nitrate also increased the contents of nitrogen, nitrogen-related metabolites, glucose, fructose, and sorbitol, but decreased the contents of several acid-related metabolites. Moreover, nitrate activated carbon and nitrogen metabolism at 25, 30, and 35 days post-anthesis (DPA). Nitrate treatment induced 10,206 differentially expressed genes (DEGs), which enriched carbon and nitrogen metabolism, amino acid, phenylpropanoid, flavonoid, terpenoid, carotenoid biosynthesis, and other metabolic pathways at 35 DPA. The DEGs also enriched GO terms for nitrate, nitrogen compound, and peptide transporter activities. Nitrate treatment significantly regulated 79 out of 164 nitrate transporter genes (FaNRTs) at 25, 30, and 35 DPA. Correlation analysis showed that strawberry adaptation to nitrate availability during fruit development involves dynamic multi-combinations between FaNRT and different TF families. qRT-PCR analysis showed that FaNPF6.3, FaNPF4.6, and FaNPF7.2 are potential nitrate signaling molecules and transporters for root nitrate uptake or removing nitrate from xylem vessels. Nitrate treatment induced FaNPF6.3, FaNPF4.6, and FaNPF7.2 expression while their correlated TFs (FaSPL8, FaNAC77-like, FaMYB1R1, and FaMYB44-like) transcription levels were down-regulated at 25 DPA. These results indicate that the spatio-temporal expression of nitrate transporters correlated with the increased nitrogen use efficiency (NUE) to enhance metabolism. The results provide a fertilizer and water management strategy for improving quality and productivity in the strawberry industry.